Method and system for heating a vehicle battery

Abstract

A method and system for heating a vehicle battery, such as the type used for vehicle propulsion in a hybrid electric vehicle (HEV). Depending on the battery chemistry involved, such batteries may not perform well in extremely cold environments. For instance, a lithium-ion battery can exhibit a high internal resistance when the battery is extremely cold, which in turn can negatively affect the available power or other capabilities of the battery. According to an exemplary embodiment, the method and system take advantage of the high internal resistance in a cold vehicle battery by purposely cycling electrical current in and/or out of the battery so that heat is created. This heat warms up the vehicle battery and thereby improves its overall performance and capabilities.

The invention claimed is: 
     
       1. A method of heating a vehicle battery used for vehicle propulsion, comprising the steps of:
 (a) sensing one or more battery conditions with battery sensors and one or more additional conditions with additional sensors, the battery conditions include a battery temperature and the additional conditions include a transmission state; 
 (b) comparing the battery temperature to a temperature threshold; and 
 (c) when the battery temperature is less than the temperature threshold and the transmission state is ‘park’, using both a charging operation and a discharging operation to rapidly cycle or oscillate a flow of electrical current into and out of the vehicle battery without regard to a torque request from a driver so as to quickly raise the battery temperature. 
 
     
     
       2. The method of  claim 1 , wherein step (b) further comprises comparing the battery temperature to a static temperature threshold that generally stays the same during the life of the vehicle battery. 
     
     
       3. The method of  claim 1 , wherein step (b) further comprises comparing the battery temperature to a dynamic temperature threshold that changes during the life of the vehicle battery in order to address changes in battery performance. 
     
     
       4. The method of  claim 1 , wherein step (a) further comprises sensing one or more battery conditions with battery sensors, the battery conditions include a battery temperature and a battery state-of-charge (SOC); and step (b) further comprises comparing the battery SOC to one or more SOC thresholds. 
     
     
       5. The method of  claim 4 , wherein if the battery state-of-charge (SOC) is greater than an upper SOC threshold and the transmission state is ‘drive’, then step (c) uses a discharging operation to both raise the battery temperature and to lower the battery SOC, and the discharging operation includes instructing a generator to provide less electrical power than is needed to fulfill a torque request for driving the vehicle. 
     
     
       6. The method of  claim 4 , wherein if the battery state-of-charge (SOC) is less than a lower SOC threshold and the transmission state is ‘drive’, then step (c) uses a charging operation to both raise the battery temperature and to raise the battery SOC, and the charging operation includes instructing a generator to provide more electrical power than is needed to fulfill a torque request for driving the vehicle. 
     
     
       7. The method of  claim 4 , wherein if the battery state-of-charge (SOC) is between a lower SOC threshold and an upper SOC threshold and the transmission state is ‘drive’, then step (c) uses both a charging operation and a discharging operation to raise the battery temperature, to maintain the battery SOC in a desired range, and to fulfill a torque request for driving the vehicle. 
     
     
       8. The method of  claim 1 , further comprising the step of:
 sensing the battery temperature following the at least one charging or discharging operation of step (c), comparing the newly sensed battery temperature to a second temperature threshold that is greater than the temperature threshold of step (b), and if the newly sensed battery temperature is less than the second temperature threshold then repeating step (c). 
 
     
     
       9. The method of  claim 1 , further comprising the step of:
 when the transmission state is ‘drive’, then determining a torque request that is representative of the torque or acceleration being requested of the vehicle, and fulfilling the torque request during the at least one of the charging operation or the discharging operation. 
 
     
     
       10. A method of heating a vehicle battery used for vehicle propulsion, comprising the steps of:
 (a) sensing one or more battery conditions with battery sensors and one or more additional conditions with additional sensors, the battery conditions include a battery temperature and the additional conditions include a transmission state; 
 (b) comparing the battery temperature to a temperature threshold, the temperature threshold is a dynamic temperature threshold that changes during the life of the vehicle battery in order to address changes in battery performance; and 
 (c) when the battery temperature is less than the temperature threshold and the transmission state is ‘park’, using both a charging operation and a discharging operation to cycle electrical current into and out of the vehicle battery without regard to a torque request from a driver such that the internal resistance of the vehicle battery causes the electrical current to raise the battery temperature. 
 
     
     
       11. The method of  claim 10 , wherein step (a) further comprises sensing one or more battery conditions with battery sensors, the battery conditions include a battery temperature and a battery state-of-charge (SOC); and step (b) further comprises comparing the battery SOC to one or more SOC thresholds. 
     
     
       12. The method of  claim 11 , wherein if the battery state-of-charge (SOC) is between a lower SOC threshold and an upper SOC threshold, then step (c) uses both a charging operation and a discharging operation to both raise the battery temperature and to maintain the battery SOC in a desired range. 
     
     
       13. The method of  claim 10 , further comprising the step of:
 sensing the battery temperature following the cycling of electrical current in step (c), comparing the newly sensed battery temperature to a second temperature threshold that is greater than the temperature threshold of step (b), and if the newly sensed battery temperature is less than the second temperature threshold then repeating step (c). 
 
     
     
       14. The method of  claim 10 , further comprising the step of:
 when the transmission state is ‘drive’, then determining a torque request that is representative of the torque or acceleration being requested of the vehicle, and fulfilling the torque request during the cycling of electrical current into and out of the vehicle battery.